host is a simple utility for performing DNS lookups. It is normally used
to convert names to IP addresses and vice versa. When no arguments or options
are given, host prints a short summary of its command line arguments
and options.

name is the domain name that is to be looked up. It can also be a
dotted-decimal IPv4 address or a colon-delimited IPv6 address, in which case
host will by default perform a reverse lookup for that address.
server is an optional argument which is either the name or IP address
of the name server that host should query instead of the server or
servers listed in /etc/resolv.conf.

The -a (all) option is equivalent to setting the -v option and
asking host to make a query of type ANY.

When the -C option is used, host will attempt to display the SOA
records for zone name from all the listed authoritative name servers
for that zone. The list of name servers is defined by the NS records that are
found for the zone.

The -c option instructs to make a DNS query of class class. This
can be used to lookup Hesiod or Chaosnet class resource records. The default
class is IN (Internet).

Verbose output is generated by host when the -d or -v
option is used. The two options are equivalent. They have been provided for
backwards compatibility. In previous versions, the -d option switched
on debugging traces and -v enabled verbose output.

List mode is selected by the -l option. This makes host perform a
zone transfer for zone name. Transfer the zone printing out the NS, PTR
and address records (A/AAAA). If combined with -a all records will be
printed.

The -i option specifies that reverse lookups of IPv6 addresses should use
the IP6.INT domain as defined in RFC1886. The default is to use IP6.ARPA.

The -N option sets the number of dots that have to be in name for
it to be considered absolute. The default value is that defined using the
ndots statement in /etc/resolv.conf, or 1 if no ndots statement is
present. Names with fewer dots are interpreted as relative names and will be
searched for in the domains listed in the search or domain
directive in /etc/resolv.conf.

The number of UDP retries for a lookup can be changed with the -R option.
number indicates how many times host will repeat a query that
does not get answered. The default number of retries is 1. If number is
negative or zero, the number of retries will default to 1.

Non-recursive queries can be made via the -r option. Setting this option
clears the RD — recursion desired — bit in the query
which host makes. This should mean that the name server receiving the
query will not attempt to resolve name. The -r option enables
host to mimic the behavior of a name server by making non-recursive
queries and expecting to receive answers to those queries that are usually
referrals to other name servers.

By default host uses UDP when making queries. The -T option makes
it use a TCP connection when querying the name server. TCP will be
automatically selected for queries that require it, such as zone transfer
(AXFR) requests.

The -4 option forces host to only use IPv4 query transport. The
-6 option forces host to only use IPv6 query transport.

The -t option is used to select the query type. type can be any
recognized query type: CNAME, NS, SOA, SIG, KEY, AXFR, etc. When no query type
is specified, host automatically selects an appropriate query type. By
default it looks for A records, but if the -C option was given, queries
will be made for SOA records, and if name is a dotted-decimal IPv4
address or colon-delimited IPv6 address, host will query for PTR
records. If a query type of IXFR is chosen the starting serial number can be
specified by appending an equal followed by the starting serial number (e.g.
-t IXFR=12345678).

The time to wait for a reply can be controlled through the -W and
-w options. The -W option makes host wait for wait
seconds. If wait is less than one, the wait interval is set to one
second. When the -w option is used, host will effectively wait
forever for a reply. The time to wait for a response will be set to the number
of seconds given by the hardware's maximum value for an integer quantity.

The -s option tells hostnot to send the query to the next
nameserver if any server responds with a SERVFAIL response, which is the
reverse of normal stub resolver behavior.

The -m can be used to set the memory usage debugging flags record,
usage and trace.

If host has been built with IDN (internationalized domain name) support,
it can accept and display non-ASCII domain names. host appropriately
converts character encoding of domain name before sending a request to DNS
server or displaying a reply from the server. If you'd like to turn off the
IDN support for some reason, defines the IDN_DISABLE environment
variable. The IDN support is disabled if the variable is set when host
runs.